import java.util.*;
/*
 public class ListNode {
    int val;
    ListNode next = null;

    ListNode(int val) {
        this.val = val;
    }
}
*/
public class Solution {

    public ListNode EntryNodeOfLoop(ListNode pHead) {
       HashSet<ListNode> set=new HashSet<>();
        while(pHead!=null){
            if(set.contains(pHead)){
                return pHead;
            }
            set.add(pHead);//加入为重复的节点
            pHead=pHead.next;
        }
        return null;
    }
}
